Method of transmitting sounding reference signal in wireless communication system

ABSTRACT

A method of transmitting a sounding reference signal includes generating a physical uplink control channel (PUCCH) carrying uplink control information on a subframe, the subframe comprising a plurality of SC-FDMA (single carrier-frequency division multiple access) symbols, wherein the uplink control information is punctured on one SC-FDMA symbol in the subframe, and transmitting simultaneously the uplink control information on the PUCCH and a sounding reference signal on the punctured SC-FDMA symbol. The uplink control information and the sounding reference signal can be simultaneously transmitted without affecting a single carrier characteristic.

TECHNICAL FIELD

The present invention relates to wireless communication, and moreparticularly, to a method of transmitting a sounding reference signal ina wireless communication system.

BACKGROUND ART

In next generation wireless communication systems, multimedia data canbe transmitted with high quality at a high speed under limited radioresources. To achieve this, spectral efficiency needs to be maximizedsince a radio channel has a limited bandwidth. In addition, inter-symbolinterference and frequency selective fading, which occur duringhigh-speed transmission, need to be overcome.

In order to improve performance of the wireless communication system, aclosed-loop transmission scheme using channel condition between a basestation (BS) and a user equipment (UE) has been introduced. An adaptivemodulation and coding (AMC) scheme improves link performance byadjusting modulation and coding scheme (MCS) by using feedback ofchannel condition information.

In general, the UE informs the BS of downlink channel condition in awell-known format, e.g., a channel quality indicator (CQI). The BS canreceive the downlink channel condition from all UEs and performfrequency selective scheduling. To perform the frequency selectivescheduling in uplink, the BS has to know uplink channel condition.

A reference signal is used to estimate the channel condition. Thereference signal is previously known to both the BS and the UE, and isalso referred to as a pilot. An uplink reference signal has two types ofsignals, i.e., a demodulation reference signal and a sounding referencesignal. The demodulation reference signal is used to estimate a channelfor data demodulation. The sounding reference signal is used in userscheduling irrespective of data transmission.

A variety of uplink control signal is transmitted on uplink controlchannel. Examples of the uplink control signal are an acknowledgment(ACK)/not-acknowledgement (NACK) signal used to perform hybrid automaticrepeat request (HARQ), a channel quality indicator (CQI) indicatingdownlink channel quality, a precoding matrix index (PMI), a rankindication (RI), etc.

Uplink transmission is performed by the UE. Thus, it is important forthe UE to have low peak-to-average power ratio (PAPR) in order todecrease battery consumption. For this, a modulation scheme having asingle carrier characteristic can be used in uplink transmission. Thesounding reference signal is not related to uplink control signal.Therefore, when the sounding reference signal is transmitted on theuplink control channel, it is difficult to preserve the single carriercharacteristic. In addition, if the uplink control signal and thesounding reference signal are separately transmitted, it is difficult toimprove spectral efficiency.

DISCLOSURE OF INVENTION Technical Problem

A method is sought for transmitting a sounding reference signal togetherwith uplink control signal in a wireless communication system.

Technical Solution

In an aspect, a method of transmitting a sounding reference signal in awireless communication system is provided. The method includesgenerating a physical uplink control channel (PUCCH) carrying uplinkcontrol information on a subframe, the subframe comprising a pluralityof SC-FDMA (single carrier-frequency division multiple access) symbols,wherein the uplink control information is punctured on one SC-FDMAsymbol in the subframe, and transmitting simultaneously the uplinkcontrol information on the PUCCH and a sounding reference signal on thepunctured SC-FDMA symbol.

The subframe may be composed of two slots, and the PUCCH may use oneresource block in each of the two slot sin the subframe. The uplinkcontrol information may be spread by orthogonal sequences with differentlengths in each of the two slots in the subframe.

In still another aspect, a method of transmitting a sounding referencesignal in a wireless communication system is provided. The methodincludes generating a physical uplink control channel (PUCCH) carryinguplink control information on a subframe, the subframe comprising afirst slot and a second slot, a slot comprising a plurality of SC-FDMAsymbols, the uplink control information spread by a first orthogonalsequence in the first slot and a second orthogonal sequence in thesecond slot, wherein the length of the first orthogonal sequence isshorter than that of the second orthogonal sequence; and transmittingthe uplink control information on the PUCCH and the sounding referencesignal on SC-FDMA symbol of the first slot.

The first orthogonal sequence may be selected from a set of orthogonalsequences [(1, 1, 1), (1, e^(j2×/3), e^(j4×/3)), (1, e^(j4×/3),e^(j2×/3))], and the second orthogonal sequence may be selected from aset of orthogonal sequences [1, 1, 1, 1), (1, −1, 1, −1), (1, −1, −1,1)].

In still another aspect, a method of receiving a sounding referencesignal in a wireless communication system is provided. The methodincludes receiving uplink control information on a physical uplinkcontrol channel (PUCCH), the PUCCH comprising a plurality of SC-FDMAsymbols, wherein one SC-FDMA symbol is punctured, and receiving asounding reference signal on the punctured SC-FDMA symbol.

Advantageous Effects

Uplink control information and a sounding reference signal can besimultaneously transmitted without affecting a single carriercharacteristic, thereby reducing battery consumption of a userequipment. In addition, spectral efficiency can be improved, and ascheduling overhead due to the transmission of the sounding referencesignal can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a transmitter according to an embodiment ofthe present invention.

FIG. 2 is a block diagram of a signal generator according to a singlecarrier-frequency division multiple access (SC-FDMA) scheme.

FIG. 3 shows a structure of a radio frame.

FIG. 4 shows an example of a resource grid for one uplink slot.

FIG. 5 shows a structure of an uplink subframe.

FIG. 6 shows a structure of an acknowledgment (ACK)/not-acknowledgement(NACK) channel in a subframe.

FIG. 7 shows a structure of a channel quality indicator (CQI) channel ina subframe.

FIG. 8 shows an example of a subframe for transmitting a soundingreference signal.

FIG. 9 shows a structure of an ACK/NACK channel that can be transmittedsimultaneously with a sounding reference signal.

FIG. 10 shows a structure of a CQI channel that can be transmittedsimultaneously with a sounding reference signal.

FIG. 11 shows an example of simultaneous transmission of a soundingreference signal and ACK/NACK information in a subframe.

FIG. 12 shows an example of two-types of physical uplink controlchannels (PUCCHs).

FIG. 13 shows an example for describing a case where a user equipment(UE) can know the presence of signaling from a base station (BS) withoutthe aid of other elements and an opposite case.

FIG. 14 shows an example of a case where a type-1 control channel and atype-2 control channel do not coexist in one subframe.

FIG. 15 shows another example of a case where a type-1 control channeland a type-2 control channel do not coexist in one subframe.

FIG. 16 shows an example for describing different types of operations.

FIG. 17 is a flow diagram of a method of transmitting a signal referencesignal by using a sounding indicator.

FIG. 18 shows an example of coexistence between a type-1 control canneland a type-2 control channel in one subframe.

FIG. 19 shows another example of coexistence between a type-1 controlchannel and a type-2 control channel in one subframe.

FIG. 20 shows an example of a scheduling method performed by a BS.

FIG. 21 shows an example of transmission of a signal reference signalwith respect to 4 UE groups.

FIG. 22 shows an example of transmission of a signal reference signalwith respect to 9 UE groups.

FIG. 23 shows another example of transmission of a signal referencesignal with respect to 9 UE groups.

FIG. 24 shows an example of transmission of a signal reference signal.

FIG. 25 shows another example of transmission of a signal referencesignal.

FIG. 26 shows a type-1 control channel and a type-2 control channel whenusing a CQI channel.

FIG. 27 shows an example of simultaneous transmission of a CQI and asignal reference signal.

FIG. 28 shows another example of simultaneous transmission of a CQI anda signal reference signal.

MODE FOR THE INVENTION

In the following disclosure, downlink represents a communication linkfrom a base station (BS) to a user equipment (UE), and uplink representsa communication link from the UE to the BS. In downlink, a transmittermay be a part of the BS, and the receiver may be a part of the UE. Inuplink, the transmitter may be a part of the UE, and a receiver may be apart of the BS. The UE may be fixed or mobile, and may be referred to asanother terminology, such as a mobile station (MS), a user terminal(UT), a subscriber station (SS), a wireless device, etc. The BS isgenerally a fixed station that communicates with the UE and may bereferred to as another terminology, such as a node-B, a base transceiversystem (BTS), an access point, etc. There are one or more cells withinthe coverage of the BS.

FIG. 1 is a block diagram of a transmitter according to an embodiment ofthe present invention.

Referring to FIG. 1, a transmitter 100 includes a sounding referencesignal generator 110, a control channel generator 120, a data processor130, a physical resource mapper 140, and a signal generator 150.

The sounding reference signal generator 110 generates a soundingreference signal. A reference signal has two types of signals, i.e., ademodulation reference signal and the sounding reference signal. Thedemodulation reference signal is used in channel estimation for datademodulation. The sounding reference signal is used in uplinkscheduling. A reference signal sequence used by the demodulationreference signal may be the same as that used by the sounding referencesignal.

The control channel generator 120 generates a physical uplink controlchannel (PUCCH) for carrying uplink control information.

The data processor 130 processes user data and thus generatescomplex-valued symbols. The physical resource mapper 140 maps thesounding reference signal, the control channel, and/or thecomplex-valued symbols for the user data onto physical resources. Thephysical resources may be resource elements or subcarriers.

The signal generator 150 generates time-domain signals to be transmittedthrough a transmit antenna 190, The signal generator 150 may generatethe time-domain signals by using a single carrier-frequency divisionmultiple access (SC-FDMA) scheme. The time-domain signal output from thesignal generator 150 is referred to as an SC-FDMA symbol or anorthogonal frequency division multiple access (OFDMA) symbol.

It will be assumed hereinafter that the signal generator 150 uses theSC-FDMA scheme. However, this is for exemplary purposes only, and thusthe present invention may also apply to other multiple-access schemes.For example, the present invention may apply to various multiple-accessschemes such as OFDMA, code division multiple access (CDMA), timedivision multiple access (TDMA), and frequency division multiple access(FDMA).

FIG. 3 is a block diagram of a signal generator according to an SC-FDMAscheme.

Referring to FIG. 2, a signal generator 200 includes a discrete Fouriertransform (DFT) unit 220 that performs DFT, a subcarrier mapper 230, andan inverse fast Fourier transform (IFFT) unit 240 that performs IFFT.The DFT unit 220 performs DFT on input data and thus outputsfrequency-domain symbols. The subcarrier mapper 230 maps thefrequency-domain symbols onto respective subcarriers. The IFFT unit 230performs IFFT on input symbols and thus outputs time-domain signals.

FIG. 3 shows a structure of a radio frame.

Referring to FIG. 3, the radio frame includes 10 subframes. One subframeincludes two slots. A time for transmitting one subframe is defined as atransmission time interval (TTI). For example, one subframe may have alength of 1 ms, and one slot may have a length of 0.5 ms. One slotincludes a plurality of SC-FDMA symbols in a time domain and a pluralityof resource blocks in a frequency domain.

The radio frame of FIG. 3 is shown for exemplary purposes only. Thus,the number of subframes included in the radio frame or the number ofslots included in the subframe or the number of SC-FDMA symbols includedin the slot may be modified in various manners.

FIG. 4 shows an example of a resource grid for one uplink slot.

Referring to FIG. 4, the uplink slot includes a plurality of SC-FDMAsymbols in a time domain and a plurality of resource blocks in afrequency domain. It is shown in FIG. 4 that one uplink slot includes 7SC-FDMA symbols and one resource block includes 12 subcarriers. However,this is for exemplary purposes only, and thus the present invention isnot limited thereto.

Each element of the resource grid is referred to as a resource element.One resource block includes 12×7 resource elements. The number NUL ofresource blocks included in the uplink slot is dependent on an uplinktransmission bandwidth determined in a cell.

FIG. 5 shows a structure of an uplink subframe.

Referring to FIG. 5, an uplink subframe is divided into a control regionassigned to a physical uplink control channel (PUCCH) for carryinguplink control information and a data region assigned to a physicaluplink shared channel (PUSCH) for carrying user data. A middle portionof the subframe is assigned to the PUSCH. Both sides of the uplinksubframe are assigned to the PUCCH. One UE does not simultaneouslytransmit the PUCCH and the PUSCH.

Example of the uplink control information transmitted on the PUCCH arean acknowledgment (ACK)/not-acknowledgement (NACK) signal used toperform hybrid automatic repeat request (HARQ), a channel qualityindicator (CQI) indicating a downlink channel condition, a schedulingrequest signal used to request uplink radio resource allocation, etc.

The PUCCH for one UE uses one resource block which occupies a differentfrequency in each of two slots in the subframe. The tow slots usedifferent resource blocks (or subcarriers) in the subframe. This is saidthat the two resource blocks assigned to the PUCCH are frequency-hoppedin a slot boundary. It is assumed herein that the PUCCH is assigned tothe subframe for 4 UEs respectively in association with a PUCCH (m=0), aPUCCH (m=1), a PUCCH (m=2), and a PUCCH (m=3).

The PUCCH can support multiple formats. That is, the uplink controlinformation having a different bit number for each subframe can betransmitted according to a modulation scheme. For example, when binaryphase shift keying (BPSK) is used, 1-bit uplink control information canbe transmitted on the PUCCH, and when Quadrature phase shift keying(QPSK) is used, 2-bit uplink control information can be transmitted onthe PUCCH.

FIG. 6 shows a structure of an ACK/NACK channel in a subframe. TheACK/NACK channel is a control channel for transmitting an ACK/NACKsignal on a PUCCH. The ACK/NACK signal is 1-bit or 2-bit uplink controlinformation. For clarity, it is assumed that one slot includes 7 SC-FDMAsymbols and one subframe includes two slots. When a control signal istransmitted in a pre-allocated band, frequency-domain spreading andtime-domain spreading are simultaneously used to increase the number ofmultiplexible UEs or the number of control channels.

Referring to FIG. 6, among the 7 SC-FDMA symbols included in one slot, ademodulation reference signal (indicated by RS in the figure) is carriedon 3 SC-FDMA symbols and the ACK/NACK signal is carried on the remaining4 SC-FDMA symbols. The demodulation reference signal is carried on 3contiguous SC-FDMA symbols. A location and the number of symbols used inthe demodulation reference signal may vary. As a result, a location andthe number of symbols used in the ACK/NACK signal may also vary. TheACK/NACK signal is a transmission and/or reception confirm signal fordownlink data.

A frequency-domain spreading code is used to spread the ACK/NACK signalin the frequency domain. A first orthogonal code is used as thefrequency-domain spreading code. A Zadoff-Chu (ZC) sequence is one ofconstant amplitude zero auto-correlation (CAZAC) sequences and is usedas the first orthogonal code. However, this is for exemplary purposesonly, and thus other sequences having excellent correlationcharacteristics can also be used. In particular, each control channelcan be identified by using a ZC sequence having a different cyclic shiftvalue.

A ZC sequence c(k) having a length of N can be generated according tothe following equation:

$\begin{matrix}{{{MathFigure}\mspace{14mu} 1}\mspace{520mu}} & \; \\{{c(k)} = \left\{ \begin{matrix}^{{- j}\frac{\pi \; {{Mk}{({k + 1})}}}{N}} & {{for}\mspace{14mu} {odd}\mspace{14mu} N} \\^{{- j}\frac{\pi \; {Mk}^{2}}{N}} & {{for}\mspace{14mu} {even}\mspace{14mu} N}\end{matrix} \right.} & \left\lbrack {{Math}.\mspace{14mu} 1} \right\rbrack\end{matrix}$

where 0≦k≦N−1, and M is a root index and is a natural number equal to orless than N, where N is relatively prime to M. This means that once N isdetermined, the number of root indices is equal to the number ofavailable ZC sequences.

The ZC sequence c(k) has three characteristics as follows.

$\begin{matrix}{{{MathFigure}\mspace{14mu} 2}\mspace{526mu}} & \; \\{{{{c\left( {{k;N},M} \right)}} = {1\mspace{31mu} {for}\mspace{14mu} {all}\mspace{14mu} k}},N,M} & \left\lbrack {{Math}.\mspace{14mu} 2} \right\rbrack \\{{{MathFigure}\mspace{14mu} 3}\mspace{526mu}} & \; \\{{R_{M,N}(d)} = \left\{ \begin{matrix}{1,} & {{{for}\mspace{14mu} d} = 0} \\{0,} & {{{for}\mspace{14mu} d} \neq 0}\end{matrix} \right.} & \left\lbrack {{Math}.\mspace{14mu} 3} \right\rbrack \\{{{MathFigure}\mspace{14mu} 4}\mspace{526mu}} & \; \\{{{R_{M_{1},{M_{2};N}}(d)} = {p\mspace{31mu} {for}\mspace{14mu} {all}\mspace{14mu} M_{1}}},M_{2}} & \left\lbrack {{Math}.\mspace{14mu} 4} \right\rbrack\end{matrix}$

Equation 2 shows that the ZC sequence always has a magnitude of ‘1’.Equation 3 shows that auto-correlation of the ZC sequence is indicatedby a Dirac-delta function. The auto-correlation is based on circularcorrelation. Equation 5 shows that cross correlation is always constant.

The ACK/NACK signal is spread over the frequency domain and is undergoneIFFT. Thereafter, the ACK/NACK signal is spread over the time domain byusing a second orthogonal code which is a time-domain spreading code.The second orthogonal code may be a Walsh code. Herein, spreading iscarried out by using 4 Walsh codes w0, w1, w2, and w3 for 4 SC-FDMAsymbols, respectively. Although the Walsh code is used as the secondorthogonal code, other codes having excellent correlationcharacteristics, such as the ZC sequence, may also be used.

Although it has been described that the frequency-domain spreading isperformed before the time-domain spreading is performed, this is forexemplary purposes only. Thus, the present invention is not limited tothe order of performing the frequency-domain spreading and thetime-domain spreading. The time-domain spreading may be performed beforethe frequency-domain spreading is performed. The time-domain spreadingand the frequency-domain spreading may be simultaneously performed byusing one sequence having a combined format.

It has been described that the ZC sequence is used as the firstorthogonal code which is the frequency-domain spreading code, and theWalsh code is used as the second orthogonal code which is thetime-domain spreading code. However, the present invention is notlimited thereto. Thus, a DFT code or other codes having excellentcorrelation characteristics may also be used.

The control information may be two-dimensionally spread over both thefrequency domain and the time domain so that more number of UEs can besupported. Assume that 6 orthogonal codes can be used through cyclicshift when the frequency-domain spreading is performed by using the ZCsequence. For 3 demodulation reference signals, a total of 6×3=18 UEscan be supported by using a DFT-based spreading code in the time domain.In this case, the ACK/NACK signal to be transmitted uses an orthogonalcode having a length of 4 as the time-domain spreading code, therebyenabling coherent detection.

FIG. 7 shows a structure of a CQI channel in a subframe. The CQI channelis a control channel for transmitting a CQI on a PUCCH.

Referring to FIG. 7, among 7 SC-FDMA symbols included in one slot, ademodulation reference signal (indicated by RS in the figure) is carriedon 2 SC-FDMA symbols spaced apart from each other by 3 SC-FDMA symbols,and the CQI is carried on the remaining 5 SC-FDMA symbols. This is forexemplary purposes only, and thus a location and the number of SC-FDMAsymbols used in the demodulation reference signal or a location or thenumber of symbols used in the CQI may vary. When QPSK mapping ispreferred on one SC-FDMA symbols, a 2-bit CQI value can be carried.Therefore, a 10-bit CQI value can be carried on one slot. For onesubframe, a maximum 20-bit CQI value can be carried. In addition to theQPSK, the CQI may use other modulation schemes, e.g., 16-quadratureamplitude modulation (QAM).

The CQI is spread over a frequency domain by using a frequency-domainspreading code. The frequency-domain spreading code may be a ZCsequence.

Unlike the two-dimensional spreading in the ACK/NACK channel, the CQIchannel uses only one-dimension spreading and thus increases CQItransmission capacity. Although only the frequency-domain spreading isdescribed herein as an example, the CQI channel may also use time-domainspreading.

A specific type of a control signal as well as other types of controlsignals can be multiplexed in one control channel. For example, both aCQI signal and an ACK/NACK signal can be multiplexed in one controlchannel.

Now, a subframe structure and a control channel structure fortransmitting a sounding reference signal will be described.

FIG. 8 shows an example of a subframe for transmitting a soundingreference signal. The subframe may be an uplink subframe.

Referring to FIG. 8, the sounding reference signal is transmitted on oneSC-FDMA symbol. There is no limit in a location and the number ofSC-FDMAs in which the sounding reference signal is arranged. Thus, thesounding reference signal may be transmitted in two or more SC-FDMAsymbols. The sounding reference signal is transmitted by a UE to a BS sothat an uplink channel response can be measured as accurately aspossible for uplink scheduling. The sounding reference signal may betransmitted one time throughout the entire uplink frequency band or maybe transmitted sequentially several times throughout a plurality offrequency bands.

The sounding reference signal occupies one SC-FDMA symbol in onesubframe. Therefore, the sounding reference signal is transmitted in anyone of two slots. Depending on systems, it is not mandatory to transmitthe sounding reference signal in every subframe. The sounding referencesignal may be periodically or non-periodically transmitted.

A UE cannot simultaneously transmit a PUCCH and a PUSCH. Therefore, theUE can simultaneously transmit the sounding reference signal and thePUCCH and also can simultaneously transmit the sounding reference signaland the PUSCH, but cannot simultaneously transmit the sounding referencesignal, the PUCCH, and the PUSCH.

The sounding reference signal can be transmitted in a specific SC-FDMAsymbol of a first slot adjacent to a second slot. This is for exemplarypurposes only, and thus the sounding reference signal may be transmittedin any SC-FDMA symbols of the first slot. For example, the soundingreference signal may be transmitted in a first SC-FDMA symbol or a lastSC-FDMA symbol in the subframe.

Orthogonality of control information transmitted on the control channelcan be maintained when neither the demodulation reference signal nor anyother control information is multiplexed in the SC-FDMA symbol on whichthe sounding reference signal is transmuted, That is, in the ACK/NACKchannel or the CQI channel, systems are managed by designing a channelformat such that none of the ACK/NACK signal, the CQI, and shedemodulation reference signal is arranged in the SC-FDMA symbol on whichthe sounding reference signal is arranged. Alternatively, the systemsare managed so that a resource region is not generated in which thecontrol information and the sounding reference signal overlap with eachother. For this, when the resource region (e.g., SC-FDMA symbol) inwhich the sounding reference signal is assigned is pre-arranged with theACK/NACK signal or the CQI, the overlapping resource region ispunctured.

It is possible to allow the sounding reference signal not to betransmitted through the resource block allocated with the PUCCH.Alternatively, the sounding reference signal may be transmitted throughthe resource block allocated with the PUCCH.

FIG. 9 shows a structure of an ACK/NACK channel that can be transmittedsimultaneously with a sounding reference signal.

Referring to FIG. 9, a sounding reference signal is transmitted on oneSC-FDMA symbol of a first slot. One of SC-FDMA symbols for transmittingan ACK/NACK signal is punctured. The ACK/NACK signal is asymmetricallyspread between two slots. This is because the ACK/NACK signal is spreadthroughout 3 SC-FDMA symbols in the first slot and is spread throughout4 SC-FDMA symbols in a second slot.

In a pair of slots, spreading is performed by using orthogonal sequenceseach having a different length. For example, in the first slot aspreading sequence (w₀, w₁, w₂) can be selected from a set of spreadingsequences [(1, 1, 1), (1, e^(j2×/3), e^(4×/3)), (1, e^(j4×3),e^(j2×3))]. In the second slot, a spreading sequence (w′₀, w′₁, w′₂,w′₃) can be selected from a set of spreading sequences [(1, 1, 1, 1),(1, −1, 1, −1), 1, −1, −1, 1)].

The sounding reference signal can use a ZC sequence and is mapped to anSC-FDMA symbol after performing IFFT. Herein, as an example of using afrequency-domain signal as the sounding reference signal, IFFT isperformed on the sounding reference signal. However, when a time-domainsignal is used as the sounding reference signal, IFFT may not beperformed.

In the ACK/NACK channel, the ACK/NACK signal is spread over both timedomain and frequency domain. Therefore, to preserve orthogonality of theACK/NACK signal, there should be no UE that transmits the ACK/NACKsignal on the SC-FDMA symbol for transmitting the sounding referencesignal. That is, in a case where the sounding reference signal and theACK/NACK signal are simultaneously transmitted, all UEs within a celluse the ACK/NACK channel having the same puncture structure.

Herein, a last SC-FDMA symbol of the first slot is punctured for thesounding reference signal. However, a location of the punctured SC-FDMAsymbol is not limited thereto. Therefore, for the sounding referencesignal, the punctured SC-FDMA symbol may be a first SC-FDMA symbol ofthe first slot or a last SC-FDMA symbol of the second slot.

FIG. 10 shows a structure of a CQI channel that can be transmittedsimultaneously with a sounding reference signal.

Referring to FIG. 10, a sounding reference signal is transmitted on oneSC-FDMA symbol of a first slot. One of SC-FDMA symbols for CQItransmission is punctured. The CQI is asymmetrically spread within onesubframe. This is because the CQI is spread throughout 4 SC-FDMA symbolsin the first slot and is spread throughout 5 SC-FDMA symbols in a secondslot.

The sounding reference signal can use a ZC sequence and is mapped to anSC-FDMA symbol after performing IFFT. Unlink in the ACK/NACK channel,the CQI is spread only over a frequency domain. Thus, even if one UEsimultaneously transmits the sounding reference signal together with theCQI, other UEs can use the existing CQI channel without alteration.Although the sounding reference signal and the CQI are simultaneouslytransmitted, it is not necessary for all UEs within the cell to use thesame structured CQI channel.

As described above, a control channel that can be transmittedsimultaneously with the sounding reference signal has a differentstructure from a control channel that cannot be transmittedsimultaneously with the sounding reference signal. The control channelthat cannot be transmitted simultaneously with the sounding referencesignal is referred to as a symmetric control channel or a type-1 controlchannel. This is because, as shown in FIGS. 6 and 7, resource regionsassigned to each of slots have the same size with respect to controlinformation. In comparison thereto, the control channel that can betransmitted simultaneously with the sounding reference signal isreferred to as an asymmetric control channel or a type-2 controlchannel. This is because, as shown in FIGS. 9 and 10, resource regionsassigned to each slot have different sizes with respect to the controlinformation.

Now, operations of a sounding reference signal and a control channelwill be described.

According to a proposed PUCCH structure, in a resource region (i.e., anSC-FDMA symbol) through which the sounding reference signal istransmitted, control information is punctured so that the controlinformation and the sounding reference signal are not simultaneouslytransmitted through the same resource region. For example, and ACK/NACKsignal and the sounding reference signal are not simultaneouslytransmitted on the same SC-FDMA symbol. Further, a CQI and the soundingreference signal are not simultaneously transmitted on the same SC-FDMAsymbol. Furthermore, a signal, in which the ACK/NACK signal and the CQIare multiplexed, and the sounding reference signal are notsimultaneously transmitted on the same SC-FDMA symbol. Herein, the term‘simultaneously’ means that signals are overlapped over time domainand/or frequency domain.

When the sounding reference signal is transmitted on a sounding SC-FDMAsymbol, only the sounding reference signal is transmitted on thesounding SC-FDMA symbol. It can be said that the sounding SC-FDMA symbolis obtained by puncturing one SC-FDMA symbol in a PUCCH. In a resourceregion affected by the transmission of the sounding reference signal, aspecific UE (in case of a CQI channel) or all UEs (in case of anACK/NACK channel) configures a control channel by using the remainingSC-FDMA symbols other than the sounding SC-FDMA symbol.

FIG. 11 shows an example of simultaneous transmission of a soundingreference signal and ACK/NACK information in a subframe.

Referring to FIG. 11, when a first UE (hereinafter, simply referred toas a ‘UE1’) transmits a sounding reference signal (hereinafter, simplyreferred to as an ‘SRS’) on a sounding SC-FDMA symbol, the UE1 does nottransmit an ACK/NACK signal on the sounding SC-FDMA symbol in order topreserve a single carrier characteristic of an SC-FDMA. Further, inorder to maintain orthogonality, other UEs cannot transmit the SRS onthe sounding SC-FDMA symbol.

When the ACK/NACK signal and the SRS are simultaneously transmitted, inorder to maintain orthogonality with respect to one UE, another controlinformation should not be transmitted at a time when another UEtransmits the sounding SC-FDMA symbol. In addition, the signals shouldnot overlap with each other in a frequency domain.

The SRS and the uplink control information (particularly, the ACK/NACKsignal) can be multiplexed and transmitted in various manners asfollows.

First Embodiment Operation of Two-types of PUCCHs

Two types of PUCCHs are defined according to coexistence with a SRS inone subframe. For example, a type-1control channel (or a symmetriccontrol channel) cannot coexist with the SRS, and a type-2 controlchannel (or an asymmetric control channel) can coexist with the SRS.

FIG. 12 shows an example of the two-types of PUCCHs. The type-1 controlchannel is a general PUCCH which is used for an ACK/NACK channel when itis not necessary to simultaneously transmit an ACK/NACK signal and theSRS in at least one resource block of an arbitrary subframe. During thesubframe in which the type-1 control channel is used, another UE cantransmit the SRS by using the resource block. The type-2 control channelis an optional PUCCH provided in consideration of the transmission ofthe SRS. A first slot includes an SC-FDMA symbol that is punctured totransmit the SRS. A spreading factor (SF) of a region for transmittingthe ACK/NACK signal is 3 in the first slot and is 4 in a second slot.

In order for a BS to successfully receive the SRS, a scheduling schemeor a predetermined rule is required so that UEs do not use both thetype-1 control channel and the type-2 control channel together in thesame resource block. Different types of control information can be usedin different resource blocks.

FIG. 13 shows an example for describing a case where a UE can know thepresence of signaling from a BS without the aid of other elements and anopposite case. If the UE in the cell knows SRS transmission timings forboth the UE itself and other UEs, additional scheduling or signaling isunnecessary. This is because the UEs can autonomously select a PUCCHtype on the basis of the SRS transmission timings. The UEs in the cellsimultaneously transmit an ACK/NACK signal and an SRS on a type-2control channel in a first subframe, and transmit the ACK/NACK signal onthe type-1 control channel in an N-th subframe. In this case, the type-1control channel and the type-2 control channel do not coexist in onesubframe.

FIG. 14 shows an example of a case where a type-1 control channel and atype-2 control channel do not coexist in one subframe. In an N-thsubframe, an SRS is not transmitted on the type-1 control channel. Whenthe type-2 control channel is used in an (N+1)-th subframe, uplinkcontrol information and the SRS can be simultaneously transmitted.

In addition, system operations can be carried out by predetermining aratio according to the types of control channels described in theembodiments of FIGS. 13 and 14. For example, if the type-1 controlchannel is used in first transmission, the type-2 control channel can beused in second and third transmissions so that a ratio of the type-1control channel to the type-2 control channel is 1:2. For anotherexample, the two types of control channels may be alternately used sothat the ratio of the type-1 control channel to the type-2 controlchannel can be 1:1 or another ratio.

FIG. 15 shows another example of a case where a type-1 control channeland a type-2 control channel do not coexist in one subframe. In an N-thsubframe, an SRS is not transmitted on the type-1 control channel. Whenthe type-2 control channel is used in the (N+1)-th subframe, uplinkcontrol information and the SRS can be simultaneously transmitted. Inthis case, since a sounding SC-FDMA symbol is not punctured in thetype-2 control channel, the SRS can be transmitted at one time on aPUCCH and a PUSCH. This is an example for showing how the SRS can betransmitted efficiently in a typical situation where a plurality ofresource blocks have to be used due to the increase in the number ofcontrol channels or where the resources blocks have to be asymmetricallyallocated at both sides of a frequency domain. In this situation, theSRS is transmitted throughout the entire band.

FIG. 16 shows an example for describing different types of operations.UEs belonging to a group 1 may use a type-1 control channel. UEsbelonging to a group 2 may use a type-2 control channel. Thus, thetype-1 control channel and the type-2 control channel can coexist in onesubframe. In this case, the SRS is transmitted through only theremaining regions (e.g., inner regions) other than regions used by thecontrol channels. The remaining regions can be defined in variousmanners. This is because the number of resource blocks used by thecontrol channels varies. Thus, the remaining regions may be defined suchthat a bandwidth of the SRS varies along with the variation of thenumber of resource blocks. Further, an arbitrary in-band may bedetermined and use din the operations. Various operation methods can beprovided to facilitate operations of a sounding band. For example, ifthe control channels use M resource blocks out of a total of N resourceblocks, the SRS is transmitted by using approximately (N−M) soundingbands. Exact adjustment a value of (N−M) may be difficult. In this case,an approximate value may be used to facilitate transmission andmultiplexing of the SRS.

A sounding indicator is a field by which a BS informs the UE of acontrol channel type. The sounding indicator may be a part of systeminformation and may be transmitted by using a broadcast channel, adownlink control channel, a radio resource control (RRC) message, etc.The sounding indicator may be periodically or occasionally transmitted.Further, the sounding indicator may be transmitted at the request of theUE or irrespective of the request of the UE.

There is not limit in a bit number of the sounding indicator. Sincetwo-types of control channels are provided, the sounding indicator canbe represented in one bit. A 1-bit sounding indicator may have a valuecorresponding to ‘ON’ or ‘OFF’, wherein ‘ON’ indicates the use of anasymmetric control channel and ‘OFF’ indicates the use of a symmetriccontrol channel. This means that, if the sounding indicator indicates‘ON’, the UE can simultaneously transmit uplink control information onthe asymmetric control channel and the SRS on a sounding SC-FDMA symbol.

FIG. 17 is a flow diagram of a method of transmitting an SRS by using asounding indicator. In step S310, a BS transmits the sounding indicatorto a UE. In step S320, the UE can perform the following operationsaccording to indications of the sounding indicator.

When the sounding indicator indicates ‘ON’ the UE operates as follows.(1) To transmit uplink control information (e.g., an ACK/NACK signal),the UE transmits the uplink control information through a PUCCH (i.e.,an asymmetric control channel) in which a sounding SC-FDMA symbol ispunctured, and simultaneously, transmits the SRS through the soundingSC-FDMA symbol. (2) If uplink data exists, the UE transmits the uplinkdata and/or a control signal through the PUSCH. However, the UE does nottransmit the uplink data or the control signal on an SC-FDMA symbolthrough which the SRS is transmitted in one subframe. A band throughwhich the SRS is transmitted in practice may be narrower than apredetermined band. Therefore, if there is a remaining resource afterthe SRS is transmitted, this may be informed so that the remainingresource can be used in data transmission.

When the sounding indicator indicates ‘OFF’, the UE operates as follows.(1) To transmit uplink control information, the UE transmits the uplinkcontrol information through a general PUCCH (i.e., a symmetric controlchannel). (2) If uplink data exists, the UE transmits the uplink dataand/or control information through a PUSCH.

FIG. 18 shows an example of coexistence between a type-1 control channeland a type-2 control channel in one subframe. A sounding SC-FDMA symbolis punctured in the type-2 control channel. Thus, an SRS can betransmitted on the sounding SC-FDMA symbol through a PUSCH and a PUCCH.The SRS is not transmitted on the type-1 control channel.

FIG. 19 shows another example of coexistence between a type-1 controlchannel and a type-2 control channel in one subframe. As the type-1control channel is added, a region is reduced in which an SRS istransmitted on a sounding SC-FDMA symbol.

Second Embodiment Scheduling performed by BS

A BS performs scheduling so that UEs do not simultaneously transmituplink control information and an SRS.

FIG. 20 shows an example of a scheduling method performed by a BS. If aUE1 intends to transmit an SRS in a specific subframe, the BS preventsthe UE1 from transmitting an ACK/NACK signal on a PUCCH in the subframe.Instead, the BS schedules so that another UE other than the UE1transmits the ACK/NACK signal in the subframe. That is, the BS schedulesso that one UE cannot simultaneously transmit the SRS in one subframeand uplink control information on a PUCCH. This can be achieved by usingadditional signaling or by transmitting a predetermined SRS.

On the contrary, if there is no need to limit the downlink transmissionfor the UE1, the BS can prevent the SRS from being transmitted in thesubframe.

Third Embodiment Operation of Single-type PUCCH

A PUCCH in use can be designed so that uplink control information and anSRS are not transmitted through the same resource region. The PUCCH hasthe same structure irrespective of whether the SRS is transmitted ornot. That is, irrespective of whether the SRS is transmitted or not, thePUCCH has a structure in which the SRS is transmitted through only aspecific resource region and the control signal is transmitted throughonly the remaining resource regions other than the specific resourceregion under the assumption that the specific resource region (e.g.,SC-FDMA symbol(s)) designated only for SRS transmission is always usedwhen the SRS is transmitted.

For this, the aforementioned asymmetric control channel structure can beused as a fixed PUCCH structure. For example, the ACK/NACK channel, afirst slot uses 3 demodulation reference signal symbol and 3 ACK/NACKsymbols, and the remaining one symbol is punctured to the dedicated forthe SRS. A second slot uses 3 demodulation reference signal symbol and 4ACK/NACK symbols.

Fourth Embodiment

UEs can be grouped into a plurality of groups, and an SRS can betransmitted based on the groups. A group of UEs that transmit the SRSdoes not transmit a control signal in a corresponding subframe.

FIG. 21 shows an example of transmission of an SRS with respect to 4 UEgroups. Herein, UEs are grouped into 4 groups (i.e., a first group, asecond group, a third group, and a fourth group). The number of UEsincluded in each group may be at least one. The 4 groups are forexemplary purposes only, and thus the present invention is not limitedthereto.

FIG. 21, it is assumed that at least one UE belong to the group 1transmits an SRS in a first subframe. In the first subframe, a controlchannel is not assigned to the UE belonging to the group 1 and isassigned to UEs belonging to the remaining groups 2, 3, and 4. The SRSis transmitted by using only a resource region except for the controlchannel. The present embodiment conforms to a rule in which a controlsignal and the SRS are not multiplexed in the same resource region.

Likewise, in a second subframe, a UE belonging to the group 2 transmitsthe SRS, and the control channel is assigned to UEs belong to the groups1, 3, and 4. In a third subframe, a UE belonging the group 3 transmitsthe SRS, and the control channel is assigned to UEs belonging to thegroups 1, 2, and 4. In a fourth subframe, a UE belonging to the group 4transmits the SRS, and the control channel is assigned to UEs belong tothe groups 1, 2, and 3.

In this manner, 4 subframes are transmitted, and thus the SRS can betransmitted for all groups.

FIG. 22, shows an example of transmission of an SRS with respect to 9 UEgroups. In comparison with the embodiment of FIG. 21, more groups (i.e.,groups 1 to 9) are provided, and more resource blocks (or simplyreferred to as RBs) are assigned to a control region.

Referring to FIG. 22, if an SRS of a group 1 is transmitted in a firstsubframe, UEs belonging to the remaining groups 2 to 9 other than thegroup 1 can transmit control information on a control channel while theSRS is transmitted. The SRS of the group 1 and the control channel ofthe remaining groups use mutually exclusive resource regions instead ofsimultaneously using the same resource region. The resource regionsallocated to the control channel for the groups 2 to 9 are shown forexemplary purposes only, and thus the present invention is not limitedto this arrangement.

If an SRS of the group 2 is transmitted in the second subframe, UEsbelonging to the remaining groups other than the group 2 can transmitthe control information on the control channel while the SRS istransmitted. Unlike in the first subframe, it can be seen that thenumber of RBs allocated to the control region decreases at both sidesand also an index of an allocated group varies in the control region.

FIG. 23 shows another example of transmission of an SRS with respect to9 UE groups.

Referring to FIG. 23, if an SRS of a group 1 is transmitted in a firstsubframe, UEs belonging to the remaining groups 2 to 9 other than thegroup 1 can transmit control information on a control channel while theSRS is transmitted. In comparison with the embodiment of FIG. 21 in afirst slot and a second slot, the control channels for the remaininggroups are symmetrically arranged in a frequency domain.

Scheduling can be performed in every subframe. Thus, the number of RBsallocated to the control region in every subframe, an index of a groupthat transmits a control signal, a location of a symbol or a group ofsymbols for transmitting the SRS, and a resource region range can beoccasionally changed.

Basically, in the aforementioned method, a configuration can be modifiedin a subframe unit, and there is a need to support this characteristic.If the number of RBs allocated to the control region changes, theresource region allocated to the SRS associated therewith may alsochange. The increase in the number of RBs allocated to the controlregion may result in the decrease in the size of the resource regionallocated to the SRS. When the resource region allocated to the SRSdecreases, a multiplexing scheme used between UEs and applied to the SRSof each UE may also change. That is, the multiplexing scheme and ahopping scheme need to be modified between the SRSs. This informationmay be delivered through downlink signaling. In addition, thisinformation may be obtained by using information regarding uplinkcontrol channel allocation.

Now, various examples of multiplexing of an SRS and uplink controlinformation and transmission f the multiplexed signal will be described.

FIG. 24 shows an example of transmission of an SRS. The controlinformation is transmitted on a type-2 control channel, andsimultaneously, the SRS is transmitted on a punctured sounding SC-FDMAsymbol. In this case, the SRS can be transmitted not only on a PUCCH butalso a PUSCH.

FIG. 25 shows another example of transmission of an SRS. A type-2control channel is used, and the SRS is transmitted throughout theentire band on a sounding SC-FDMA symbol.

FIG. 26 shows a type-1 control channel and a type-2 control channel whenusing a CQI channel. The type-1 control channel is a general PUCCH thatis used by a CQI when the SRS does not need to be transmitted. During asubframe in which the type-1 channel is used, other UEs cannot transmitthe SRS throughout the entire bandwidth. The type-2 control channel isan optional PUCCH provided in consideration of the transmission of theSRS. If the SC-FDMA symbol punctured for the transmission of the SRS isarranged in a first slot, the number of SC-FDMA symbol used for CQItransmission is 4 in the first slot and 5 in a second slot.

FIG. 27 shows an example of simultaneous transmission of a CQI and anSRS. A sounding SC-FDMA symbol is puncture din a type-2 control channel.Thus, the SRS can be transmitted on the sounding SC-FDMA symbol througha PUSCH and a PUCCH. The SRS is not transmitted through a region exceptfor the type-2 control channel. Only a UE that transmits the SRS usesthe type-2 control channel. Other UEs can transmit the CQI on a type-1control channel.

FIG. 28 shows another example of simultaneous transmission of a CQI andan SRS. A sounding symbol is punctured in a type-2 control channel.Thus, the SRS can be transmitted on the sounding SC-FDMA symbol througha PUSCH. Only a UE that transmits the SRS uses the type-2 controlchannel. Other UEs can transmit CQI on a type-1 control channel.

If the CQI and the SRS are simultaneously transmitted, the type-1control channel and the type-2 control cannel can always coexist in onesubframe. This provides convenience in terms of scheduling performed bya BS.

Unlike ACK/NACK, the CQI requires that the SC-FDMA symbol is puncturedonly for a user which simultaneously transmits the SRS and the CQI.Another user which shares the same puncture location can transmit theCQI in a typical format without having to puncture and without affectingorthogonality. Therefore, system operations can be further facilitatedin comparison with the case where the ACK/NACK and the SRS aresimultaneously transmitted.

The steps of a method described in connection with the embodimentsdisclosed herein may be implemented by hardware, software or acombination thereof. The hardware may be implemented by an applicationspecific integrated circuit (ASIC) that is designed to perform the abovefunction, a digital signal processing (DSP), a programmable logic device(PLD), a field programmable gate array (FPGA), a processor, acontroller, a microprocessor, the other electronic unit, or acombination thereof. A module for performing the above function mayimplement the software. The software may be stored in a memory unit andexecuted by a processor. The memory unit or the processor may employ avariety of means that is well known to those skilled in the art.

As the present invention may be embodied in several forms withoutdeparting from the spirit or essential characteristics thereof, itshould also be understood that the above-described embodiments are notlimited by any of the details of the foregoing description, unlessotherwise specified, but rather should be construed broadly within itsspirit and scope as defined in the appended claims. Therefore, allchanges and modifications that fall within the metes and bounds of theclaims or equivalence of such metes and bounds are intended to beembraced by the appended claims.

What is claimed is:
 1. A method for transmitting uplink signals in awireless communication system, the method comprising: receiving, by auser equipment (UE), a message from a base station, the messageincluding a sounding indicator indicating whether the UE is configuredto support a simultaneous transmission of an uplink control signal on aphysical uplink control channel (PUCCH) and a sounding reference signal(SRS) in a sounding subframe, the sounding subframe comprising twoslots, each slot comprising a plurality of single carrier-frequencydivision multiple access (SC-FDMA) symbols; selecting, by the UE, a typeof the PUCCH from a symmetric control channel and an asymmetric controlchannel in according with the sounding indicator; and transmitting, bythe UE, the uplink control signal on the selected type of the PUCCH inthe sounding subframe, wherein a single SC-FDMA symbol of the two slotsin the sounding subframe is reserved for the transmission of the SRS ifthe sounding indicator indicates that the UE is configured to supportthe simultaneous transmission of the uplink control signal on the PUCCHand the SRS in the sounding subframe.
 2. The method of claim 1, whereinthe single SC-FDMA symbol of the two slots in the sounding subframe isnot reserved for the transmission of the SRS if the sounding indicatorindicates that the UE is configured not to support the simultaneoustransmission of the uplink control signal on the PUCCH and the SRS inthe sounding subframe
 3. The method of claim 1, wherein selecting thetype of the PUCCH includes: selecting the asymmetric control channel asthe type of the PUCCH if the sounding indicator indicates that the UE isconfigured to support the simultaneous transmission of the uplinkcontrol signal on the PUCCH and the SRS in the sounding subframe; andselecting the symmetric control channel as the type of the PUCCH if thesounding indicator indicates that the UE is configured not to supportthe simultaneous transmission of the uplink control signal on the PUCCHand the SRS in the sounding subframe.
 4. The method of claim 1, whereinone of the two slots is spread by a first orthogonal sequence having afirst spreading factor and the other of the two slots is spread by asecond orthogonal sequence having a second spreading factor.
 5. Themethod of claim 4, wherein the symmetric control channel uses samespreading factors in the two slots of the sounding subframe but theasymmetric control channel uses different spreading factors in the twoslots of the sounding subframe.
 6. The method of claim 5, wherein thefirst and second spreading factors for the symmetric control channelhave values of four.
 7. The method of claim 6, wherein the firstspreading factor for the asymmetric control channel has a value of fourand the second spreading factor for the asymmetric control channel has avalue of three.
 8. The method of claim 1, wherein the uplink controlsignal is a channel quality information (CQI) or an acknowledgment(ACK)/non-acknowledgment (NACK) signal for a hybrid automatic repeatrequest (HARQ).
 9. A user equipment (UE) for a wireless communicationsystem, the user equipment comprising: a memory configured to storeinstructions; and a processor configured to execute the instructions andcause the user equipment to: receive a message from a base station, themessage including a sounding indicator indicating whether the UE isconfigured to support a simultaneous transmission of an uplink controlsignal on a physical uplink control channel (PUCCH) and a soundingreference signal (SRS) in a sounding subframe, the sounding subframecomprising two slots, each slot comprising a plurality of singlecarrier-frequency division multiple access (SC-FDMA) symbols; select atype of the PUCCH from a symmetric control channel and an asymmetriccontrol channel in according with the sounding indicator; and transmitthe uplink control signal on the selected type of the PUCCH in thesounding subframe, wherein a single SC-FDMA symbol of the two slots inthe sounding subframe is reserved for the transmission of the SRS if thesounding indicator indicates that the UE is configured to support thesimultaneous transmission of the uplink control signal on the PUCCH andthe SRS in the sounding subframe.
 10. The UE of claim 9, wherein thesingle SC-FDMA symbol of the two slots in the sounding subframe is notreserved for the transmission of the SRS if the sounding indicatorindicates that the UE is configured not to support the simultaneoustransmission of the uplink control signal on the PUCCH and the SRS inthe sounding subframe
 11. The UE of claim 9, wherein the processor isconfigured to select the type of the PUCCH by: selecting the asymmetriccontrol channel as the type of the PUCCH if the sounding indicatorindicates that the UE is configured to support the simultaneoustransmission of the uplink control signal on the PUCCH and the SRS inthe sounding subframe; and selecting the symmetric control channel asthe type of the PUCCH if the sounding indicator indicates that the UE isconfigured not to support the simultaneous transmission of the uplinkcontrol signal on the PUCCH and the SRS in the sounding subframe. 12.The UE of claim 9, wherein one of the two slots is spread by a firstorthogonal sequence having a first spreading factor and the other of thetwo slots is spread by a second orthogonal sequence having a secondspreading factor.
 13. The UE of claim 12, wherein the symmetric controlchannel uses same spreading factors in the two slots of the soundingsubframe but the asymmetric control channel uses different spreadingfactors in the two slots of the sounding subframe.
 14. The UE of claim13, wherein the first and second spreading factors for the symmetriccontrol channel have values of four.
 15. The UE of claim 14, wherein thefirst spreading factor for the asymmetric control channel has a value offour and the second spreading factor for the asymmetric control channelhas a value of three.
 16. The UE of claim 9, wherein the uplink controlsignal is a channel quality information (CQI) or an acknowledgment(ACK)/non-acknowledgment (NACK) signal for a hybrid automatic repeatrequest (HARQ).